Abstract
The ability of cochlear implant users to discriminate a change in spectral shape was investigated in listeners with Nucleus CI24M and CI24R(CS) implants. A primary independent variable was the number of active electrodes. Listeners were asked to detect a current increment to one of 3, 7, 11, and 21 active electrodes. Intensity discrimination on one electrode was also evaluated. Stimulation was achieved using a monopolar configuration with 75μs/phase biphasic pulses and a 24 μs interphase gap presented at 250 pps per channel. The pulses were swept in rapid succession from the base to the apex such that the overall rate increased with the number of active electrodes. Sensitivity to differences in spectral shape decreased with increasing number of electrodes. Next, the pulse rate was reduced to 159 pps per channel for the 11 and 21 active electrode conditions. Sensitivity to spectral shape at the slower pulse rate was better than that at the higher rate given the same number of active electrodes. The improvement in sensitivity with the slower rate suggests that forward masking of one pulse over a successive pulse diminishes listener’s ability to hear an intensity increment in the spectral profile.
Published Version
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